The symbiote was captured in ASM 258 and was shown in almost all issues afterward leading up to Web #1(ASM 259-261, Spec 97-100, MTU 148) and also Fantastic Four 274. I believe it escapes in ASM 261 and is shown bonding with random New Yorkers in Spec 99 and 100 before it finds Spidey in Web 1.

Wasn't Doom's ward Kristoff the one that released the symbiote from the Fantastic Four's base?

I always found it weird that Kristoff's role in unleashing the symbiote upon the world was never really referenced again.